my @bytes = map { sprintf('%02X', $_) } 0..255;

foreach my $i (@bytes) {
foreach my $j (@bytes) {
foreach my $k (@bytes) {
foreach my $l (@bytes) {
foreach my $m (@bytes) {
foreach my $n (@bytes) {
   print("$i$j$k$l$m$n\n");
}}}}}}

##</code><code>##

use Algorithm::Loops qw( NestedLoops );

my @bytes = map { sprintf('%02X', $_) } 0..255;

my $num_bytes = 6;

NestedLoops(
   [ ( [ @bytes ] ) x $bytes ],
   sub {
      print(join('', @_), "\n");
   }
);